Wireless communication has extensive applications in consumer and business markets. Among the many communication applications/systems are: fixed wireless, unlicensed (FCC) wireless, local area network (LAN), cordless telephony, personal base station, telemetry, mobile wireless, and other digital data processing applications. While each of these applications utilizes spread spectrum communications, most utilize unique a pilot signal in the communication protocol. However, the code space for the pilot signal can vary significantly depending upon the communication protocol specifying the pilot signal. Consequently, each application may utilize unique hardware, software, and methodologies for searching for the pilot signal. This practice can be costly in terms of design, testing, manufacturing, and infrastructure resources. As a result, a need arises to overcome the limitations associated with the varied hardware, software, and methodology of searching for pilot signals in each of the varied wireless applications.
Wireless devices that communicate to each other can be classified as either a base station or a handset, wherein a base station is usually fixed and acts as a hub to communicate with multiple handsets, which are sometimes mobile. Depending upon the application, the base station, the handset, or both, transmit a pilot signal. A searcher is utilized to find strong pilot signals of nearby base stations surrounding a given mobile handset. In a spread spectrum system, base stations as well as some handsets, transmit a standardized pilot signal having a known sequence of binary digits to aid in communication of data signals. These pilot signals can have a wide variety of codes, as determined by a specific communication protocol.
For example, in one protocol a pilot signal has a length of 215 (32,768) bits (or chips). This known sequence is referred to as a short pseudonoise (PN) sequence for the Industry Standard-95 (IS-95) protocol version of the CDMA system. Because all the base stations configured for this protocol transmit the same PN signal over the same bandwidth, they distinguish themselves by transmitting the PN signal with a unique offset, or phase, relative to each other. For IS-95, the phase offset for base stations is 512 chips, or code bits. Given the noise-like quality of the PN sequences, only by replicating the phase of the known PN sequence precisely, e.g., within about 1 chip, will a communication device detect the pilot signal, thereby indicating the existence of a nearby base station. Thus a need arises to accurately determine the phase of the pilot signal for a communication device, such as a base station.
Because of the width of the code space and the lack of initial synchronization between two communication devices, the specific phase offset of a pilot signal can be anywhere within the code space. That is, when a handset is first turned on, there is no synchronization between the handset and a base station. For example, a pilot sequence can have a phase offset anywhere within the pilot code space.
Unfortunately, if the offset between a base station and a handset is near the end of a long chip sequence, then it could consume significant iterations in a searcher to finally identify the precise phase offset. Although the cycle time of a cellular device is very short, the large number of iterations required can consume a relatively significant amount of time. When an operator powers up a communication device, the few seconds required for searching and acquiring a pilot signal can be significant in some applications. Again, as user sophistication increases, demand for improved performance also increases. Consequently, a need arises for a method to overcome the speed limitations of a conventional search for finding a pilot signal phase offset.